iio:bmi160: use iio_pollfunc_store_time

Currently, we snap the timestamp after reading from the buffer and
processing the event. When the IIO poll function is triggered by an
interrupt,  we can get a slightly more accurate timestamp by snapping it
prior to reading the data, since the data was already generated prior to
entering the trigger handler. This is not going to make a huge difference,
but we might as well improve slightly.

Do this by using iio_pollfunc_store_time as other drivers do.
Signed-off-by: Martin Kelly <martin@martingkelly.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/bmi160/bmi160_core.c

@@ -425,8 +425,7 @@ static irqreturn_t bmi160_trigger_handler(int irq, void *p)
 		buf[j++] = sample;
 	}
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buf,
-					   iio_get_time_ns(indio_dev));
+	iio_push_to_buffers_with_timestamp(indio_dev, buf, pf->timestamp);
 done:
 	iio_trigger_notify_done(indio_dev->trig);
 	return IRQ_HANDLED;
@@ -834,7 +833,8 @@ int bmi160_core_probe(struct device *dev, struct regmap *regmap,
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->info = &bmi160_info;
 
-	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
+	ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+					      iio_pollfunc_store_time,
 					      bmi160_trigger_handler, NULL);
 	if (ret < 0)
 		return ret;